Răspuns:
Explicație:
l=5m
s= 0,5mm²=0.5*10^-6m^2=5*10^-7m^2
U=1,28V
delta t=1s
ρ cupru=1.68*10^-8 Ω*m (extra)
N=?
_______________
R=ρ*l/s=1.68*10^-8 *5 /5*10^-7=1.68*10^-1=0.168Ω
I=U/R=1.28/0.168=7.6 A
I=Q/delta t deci Q=I delta t=7.6 *1 C
Q=N*e deci N=Q/e=7.6/1.6*10^-19 =4.75*10^19 electroni